One-Pot Synthesis of 2‑R‑Naphtho[2,3‑b]thiophene-4,9-diones via Cyclization of 2‑(R‑Ethynyl)-1,4-naphthoquinones with Na2S2O3

The concise and efficient one-pot synthesis of 2-R-naphtho­[2,3-b]­thiophene-4,9-diones from 2-bromo-1,4-naphthoquinone and alkynes has been developed. The reaction proceeds through the formation of 2-(R-ethynyl)-1,4-naphthoquinones, which undergo transformation with Na2S2O3 to 2-R-naphtho­[2,3-b]­thiophene-4,9-diones via C–H sulfuration, accompanied by the formation of the aromatic Bunte salt, followed by its air oxidation and 5-endo-dig cyclization. The protocol is characterized by simplicity, good tolerance for functional groups, relatively mild conditions, and commercially available starting compounds.